Abstract : This is an investigation into the effects of certain variables on the performance of man doing a precise superposition task. This simulates the task that the Project Apollo navigator will be required to perform during the mid-course (translunar and transearth) phases of the proposed lunar excursion. For this investigation, the Apollo Sextant Simulator was used. The variables were (1) Rate of spacecraft motion, (2) Magnification of sextant telescope, (3) Orientation of landmark, and (4) Star-landmark contrast ratio. In order to determine the effect of each variable individually, only one was varied at a time. Three subjects were used. Each performed the superposition task by using a set of hand controllers until the star was on top of the landmark, as seen through the sextant telescope. Results indicate that two of the four variables investigated have a statistically significant effect on the accuracy.